42 PROCEEDINGS OF THE ACADEMY OF [Jan., 



respect, the form from Cold Spring Harbor agrees with Professor 

 Marsh's description." The above extract needs no comment. 

 Herrick assigns C. varicans a place among the twelve-jointed-antennse 

 forms having a ^wo-segmented fifth foot. This may account for 

 Miss Byrnes' error, for Herrick's drawing of the fifth foot of C. varicans 

 is quite incorrect. 



C. varicans is one of the rarer species of the genus. Schmeil 

 foiind it sparingly in the vicinity of Halle. Lilljeborg reports it and 

 •describes it from Sweden. Herrick found it but once, and Miss 

 Byrnes also collected it in a single instance from a pond on Long 

 Island, describing it as a twelve-jointed variation of C. bicolor. In 

 his summary of species Forbes records it as "a fairly common species 

 throughout the range of Cyclops in North America." I have found 

 it in small numbers in the March and April, 1909, collections in this 

 locality and sparingly in the vicinity of Cambridge, Mass., and 

 from Lake Winnepesaukee collections taken in July and August, 1909. 



Specific Description. — The first segment of the almost elliptical 

 cephalothorax (PI. Ill, fig. 6) is about as long as wide and a little 

 over half as long as the entire thorax (3 : 5). The lateral angles of 

 the third, fourth, and especially the fifth thoracic segments are 

 prominent. The proportion of cephalothorax and abdomen is as 

 10 : 7. The posterior borders of all the thoracic segments are 

 smooth. The fifth segment is somewhat flattened and extended 

 laterally. Its lateral edges protrude considerably beyond the first 

 abdominal seghient. At the ends of these wing-like projections of 

 the fifth thoracic segment are inserted long, curving, plumose setse, 

 which are usually considered homologous to the outer setse of the 

 basal segments of the two-jointed rudimentary fifth feet. The 

 fifth feet are inserted at the inner corners of the lateral projections 

 of the fifth thoracic segment on its posterior edge (PL III, fig. 9). 



The first abdominal segment is considerably expanded in its 

 anterior half (PI. Ill, figs. 6 and 10). The entire abdomen, which 

 is rather slim, tapers gradually to the furca. The posterior borders 

 of the first three segments are smooth. On the posterior edge of 

 the fourth abdominal segment, ventrally placed and rarely extending 

 half way around the circumference of the segment, there is present 

 a short row of long serrations. 



The stylets (PI. Ill, fig. 7) taper slightly and are carried very 

 close together. They are slightly shorter than the last two abdominal 

 segments taken together. The outer apical bristle is rather heavy, 

 sparsely plumose, and nearly as long as the delicate inner one. Of 



